The First Cytogenetic Data on Strumigenys louisianae Roger, 1863 (Formicidae: Myrmicinae: Dacetini): The Lowest Chromosome Number in the Hymenoptera of the Neotropical Region

Abstract

In the present study, the first cytogenetic data was obtained for the ant species Strumigenys louisianae, from a genus possessing no previous cytogenetic data for the Neotropical region. The chromosome number observed was 2n = 4, all possessing metacentric morphology. Blocks rich in GC base pairs were observed in the interstitial region of the short arm of the largest chromosome pair, which may indicate that this region corresponds to the NORs. The referred species presented the lowest chromosome number observed for the subfamily Myrmicinae and for the Hymenoptera found in the Neotropical region. Observation of a low chromosome number karyotype has been described in Myrmecia croslandi, in which the occurrence of tandem fusions accounts for the most probable rearrangement for its formation. The accumulation of cytogenetic data may carry crucial information to ensure deeper understanding of the systematics of the tribe Dacetini.

Cytogenetics of Strumigenys louisianae Roger, 1863 (Formicidae: Myrmicinae) from North-eastern Amazonia shed light on a difficult species complex

“…Strumigenys louisianae from the Amazon rainforest showed 2n = 26 chromosomes and karyomorphometrical analysis revealed that the karyotype consists of m, sm and st chromosomes with diploid karyotypic formula 12m + 12sm + 2st (Table 2, Figure 2). The species presented a quite distinct chromosome number from that of the Atlantic rainforest population (2n = 4, all metacentrics, see Alves-Silva et al, 2014). The chromosome size of the largest chromosome pair (the single st pair) showed its size 2.5x larger than the second largest chromosome pair (1 st m pair) corresponding to a notable size difference in the karyotype (Table 2, Figure 3).…”

“…In this study, we described the karyotype of S. louisianae from Oiapoque, state of Amapá, Brazil, in north-eastern Amazonia and compared it with the available karyotype from the population of the Atlantic rainforest (Alves-Silva et al, 2014). We also highlighted morphological differences between the two populations and discussed the taxonomic importance of our results.…”

“…Cytogenetic data in the Neotropics are restricted to two species (Table 1), Strumigenys diabola Bolton, 2000 from the Amazon rainforest, 2n = 40 (Aguiar et al, 2020) and Strumigenys louisianae Roger, 1863 from Atlantic rainforest with 2n = 4, the latter having all metacentrics and corresponding to the smallest chromosome number observed in Myrmicinae (Alves-Silva et al, 2014).…”

“…The population from the Atlantic rainforest (2n = 4)(Alves-Silva et al 2014) on the other hand, is one of the most common morphotypes of Strumigenys in the locality where the karyotyped colony was found. Morphologically similar populations occur in a few other localities in the state of Minas Gerais, as well as other states from southern Brazil.…”

First Cytogenetic Study Through Conventional Staining of The Ant Genus Blepharidatta Wheeler, 1915 (Hymenoptera: Formicidae: Attini)

“…The huge variation in chromosome number ranging from 2n = 2 to 2n = 120 (Lorite & Palomeque, 2010) may provide good models to investigate the role of chromosomal variation in speciation. The Attini tribe alone currently comprises 48 genera with a total of 2.703 valid species, but there is cytogenetic information for only 21 genera (Cardoso et al, 2018) with karyotypes ranging from 2n = 4 to 2n = 64 (Alves-Silva et al, 2014;Murakami et al, 1998;Barros et al, 2013;Mariano et al, 2019;Cardoso & Cristiano, 2021). This means that the karyotypes of 56.25% of the Attini genera, such as Blepharidatta, are unknown.…”